Large loads, such as earth station antennas, have been rotated using a linear actuator, such as the extending rod of a hydraulic or pneumatic cylinder or a linear actuator screw. Conventionally, the linear actuator has been fixed at one end to an anchor pivot while the other end is attached to an arm extending from the anchor pivot of the driven load. As the actuator rod or screw extends and retracts, it rotates the driven load.
In such prior system, loss of moment arm near the extremes of travel of the actuator limits the maximum practical angle through which the load may be driven. Also, the size and strength of the actuator screw or rod must be selected to provide sufficient column stability of the actuator at full extension. This results in an inefficient, over-built mechanism for operation between the extremes of travel.
Thus a need has existed for a linear actuator which provides continuous rotational motion through angles of 180 degrees or more, which minimizes loss of moment arm at the extremes of rotational travel, and which does not depend for its strength upon column stability of the actuator at full extension thereof.